The invention relates generally to satellite antenna systems, and more particularly to an adaptive satellite antenna system for use on a radio subscriber unit.
Many types of radio subscriber units, such as cell phones, incorporate circuitry for receiving signals from satellites, such as GPS (Global Positioning System) signals, as well as circuitry for communicating signals with satellites. Numerous antenna systems and configurations are known in the prior art. For example, an antenna system operating in a diversity mode has a first antenna and a second antenna. First and second signals of a composite radio frequency signal are received from the first and second antennas, respectively. The composite radio frequency signal includes a desired radio frequency signal as well as interfering signals. The ratio of the desired signal to the estimate of the composite radio frequency signal is determined in response to receiving the desired signal of the composite radio frequency signal and a signal representative of the composite radio frequency signal. A selected state of the first antenna and the second antenna is controlled as a function of the ratio and an integrated received signal is provided that is representative of the composite radio frequency signal. See, for example, U.S. Pat. No. 6,023,615. In a switched diversity antenna apparatus, such as disclosed in U.S. Pat. No. 6,018,651, a receiver is selectively coupled to the first antenna and/or the second antenna. A controller selectively couples the receiver in response to the received signal. In a switched antenna diversity apparatus the receiver may be attached to only one of the first or second antennas, or may be attached to both of the first and second antennas.
It is a drawback in the prior art that the above-described antenna systems only operate in a diversity mode.
Antenna systems are also known which are directional, referred to, for example, as directive pattern mode, pattern gain mode, specular mode, line of sight mode, etc. Such antennas have antenna patterns with lobes that define regions in the radiation pattern in which radiation is most intense or, in which reception is strongest. An antenna array is a directional antenna that consists of an assembly of properly dimensioned and spaced elements, such as radiators, directors and reflectors.
For each of diversity mode antennas and directional antennas, the antenna elements may take on various forms, such as patch antenna structures and helical antenna structures. These antennas can take the form of quadrifilar helix, and stack patched antennas. A quadrifilar helical antenna is a highly resonant antenna, and consists of four helical arms placed at 90 degrees to one another.
In a given environment several propagation modes can be experienced. A high attenuation mode is exemplified by lite in-building fading from buildings made, for example, of wood. In this situation relatively high losses cause a reduced link margin and possibly a loss of the link with the satellite. In a highly scattered environment, a quadrifilar helix antenna has reduced performance because the antenna does not provide any diversity gain. This can also lead to a loss of the link with the satellite.
In the prior art it is known for the transmission and reception of signals with satellites to use one element for transmission and a separate element for reception. However, the known antenna systems for radio subscriber units in the prior art develop problems with different locations and conditions (such as inside or outside of buildings) when receiving satellite signals. Accordingly, there exists a need for an antenna apparatus that can adapt to changing environmental conditions.